BATTERIES 



carbon pole is oxidised into H 2 by the nitric acid, 

 of the battery is l - 9 volts. 



The E.M.F. 



Fig. 3. —The Bunsen Battery. (McKendrick.) 



The Grove Battery (fig. 4) is similar to the Bunsen battery, but 

 the carbon is replaced by a sheet of platinum. Its E.M.F. is 1'96 

 volts. 



The Leclanche Battery (fig. 5) consists of a glass jar containing a 

 saturated solution of ammonium chloride into which an amalgamated 

 zinc rod dips. This forms the 

 negative terminal. The positive 

 consists of a carbon plate fitted 

 into a porous pot packed with 

 small pieces of carbon mixed 

 with manganese dioxide. The 

 porous pot is then filled up with 

 the ammonium chloride solu- 

 tion. Its E.M.F. when freshly 

 prepared is 1*48 volts. It has 

 the disadvantage that it tends 

 to polarise rather quickly, and 

 is therefore only used when a 



current is required for short periods of time. It is very convenient, 

 as it does not fume ; there are no acids to be spilt, and it does not 

 require much attention. 



b2 



Fig. 4. — The (trove Battery. 



